1. Technical Field
This application relates to computer storage devices, and more particularly to the field of scheduling jobs for computer storage devices.
2. Description of Related Art
Host processor systems may store and retrieve data using a storage device containing a plurality of host interface units (host adapters), disk drives, and disk interface units (disk adapters). Such storage devices are provided, for example, by EMC Corporation of Hopkinton, Mass. and disclosed in U.S. Pat. No. 5,206,939 to Yanai et al., U.S. Pat. No. 5,778,394 to Galtzur et al., U.S. Pat. No. 5,845,147 to Vishlitzky et al., and U.S. Pat. No. 5,857,208 to Ofek. The host systems access the storage device through a plurality of channels provided therewith. Host systems provide data and access control information through the channels to the storage device and the storage device provides data to the host systems also through the channels. The host systems do not address the disk drives of the storage device directly, but rather, access what appears to the host systems as a plurality of logical disk units. The logical disk units may or may not correspond to the actual disk drives. Allowing multiple host systems to access the single storage device unit allows the host systems to share data stored therein.
In some cases, a disk adaptor (DA) may have multiple devices (disk drives) coupled thereto. A plurality of sources provide requests for service (jobs) to a DA which then parses and schedules the jobs by, for example, providing appropriate commands to the disk drives corresponding to read requests, write requests, etc. At certain times, jobs may be posted to a DA faster than the jobs can be processed in real time. It is desirable to provide a system that optimizes processing of jobs to provide acceptable throughput while still maintaining appropriate response times for jobs posted to a DA.